Personally, I don't like the idea, and have never done it. The risk in my eyes, is that it's not a closed system. You are flushing debris that has been exposed to room air back into the wound!!
I have dealt with thousands of JP's as a community RN, and the best way to keep JP's from blocking up is to have the patient strip the tubing every couple of hours. It's flexible, so they can grab it between their fingers, and milk it in the direction of the bulb.
Now, hemovacs...whole different story! I hate hemovacs. You cannot strip the tubing, and they are very prone to air leaks. I have had to detach the vac from the tubing to clear blood clots. Often when you do this, a long, stringy blood clot will be sticking out of the drain. If you can grab hold of the clot with a sterile piece of gauze, often you can clear the drain by gently pulling it out. Now, the nexty problem is re-attaching the drain so that the system will still keep suction. Good luck!